Dolomite (shown here with magnesite) is an anhydrous carbonate mineral composed of calcium magnesium carbonate. It forms white, tan, gray, or pink crystals, which do not react with dilute hydrochloric acid. Termed "stinking stone" by naturalist Belsazar Hacquet, the mineral gives the smell of petroleum when rubbed. It has multiple uses, including as a radiation buffer and a catalyst for destruction of tar.Photograph: Didier Descouens